Tracing high-pressure metamorphism in marbles: Phase relations in high-grade aluminous calcite–dolomite marbles from the Greek Rhodope massif in the system CaO–MgO–Al2O3–SiO2–CO2 and indications of prior aragonite

Four different types of parageneses of the minerals calcite, dolomite, diopside, forsterite, spinel, amphibole (pargasite), (Ti–)clinohumite and phlogopite were observed in calcite–dolomite marbles collected in the Kimi-Complex of the Rhodope Metamorphic Province (RMP). The presence of former aragonite can be inferred from carbonate inclusions, which, in combination with an analysis of phase relations in the simplified system CaO–MgO–Al2O3–SiO2–CO2 (CMAS–CO2) show that the mineral assemblages preserved in these marbles most likely equilibrated at the aragonite–calcite transition, slightly below the coesite stability field, at ca. 720 °C, 25 kbar and aCO2 ~ 0.01. The thermodynamic model predicts that no matter what activity of CO2, garnet has to be present in aluminous calcite–dolomite-marble at UHP conditions.